Stringent emissions standards in Europe and North America are requiring automakers to reduce emissions produced by vehicles. Various technologies have been developed to reduce these emissions.
For instance, some diesel engines exhibit high levels of nitrogen oxide (NOx) emissions. Selective catalytic reduction (SCR) approaches have been used to convert nitrogen oxides into nitrogen, N2, and water, H2O.
In SCR approaches, a reduction delivery unit (RDU) is used to inject a Diesel Exhaust Fluid (DEF) reductant into the exhaust stream of an engine. For example, urea is added to the exhaust gas stream by the RDU and various byproducts such as carbon dioxide and water are formed. Ammonia is a desired bi-product and in conjunction with a catalyst converts the nitrogen oxide (NOx) into harmless water and nitrogen.
The RDU has a DEF injector that is in some cases liquid cooled by a liquid jacket. A hot soak condition occurs when the vehicle is running but is then turned off and no liquid coolant is flowing through the jacket. During hot soak conditions, the heat of the exhaust system is conducted into the RDU. Where the vehicle is run at a high load then turned off, this hot soak can boil the coolant creating unrestricted temperatures within the RDU and subsequent over temping of DEF within the injector. When the DEF is over-temped, it forms hard insoluable byproducts that negatively affect the performance of the DEF injector.
DEF also freezes at a higher temperature than the coolant. In such circumstances, a warmed urea could be frozen during its travel through a DEF injector when intimate contact exists between the jacket and the body of the valve, and where the coolant temperature is below the freezing point of DEF.
To the extent these problems have even been addressed, the above-mentioned problems have been addressed inadequately by previous approaches. Consequently, some user dissatisfaction has been created.
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